If sent to the US, Mr McKinnon was likely to receive a substantial prison sentence and was unlikely to be repatriated to serve his sentence, Mr Fitzgerald said.

And the process of extradition, trial and sentence would expose Mr McKinnon to "an avoidable and unnecessary risk of serious psychological suffering" with "all of the attendant disastrous consequences," he added.

This application for judicial review at the High Court in London is the second recent legal challenge in Mr McKinnon's case.

In the first, Mr Fitzgerald accused the home secretary of reaching a "flawed" decision, following medical evidence of the severe mental suffering that extradition would cause.

The judges are expected to give their ruling in both legal challenges later this month.

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